<algorithm> transform modification

[Steffen Brinkmann]

Hi!

I tried to modify the transform algorithm in a way that it doesn't
take iterators, but a reference to a container class and a value,
because Mostly I need to do an operation of a container and a single
number (e.g. multiply all the values in a vector by 3 or so).
So, this is my intent:

#ifndef ALGORITHM_EXT_H H
#define ALGORITHM_EXT_H H

#include<iterat or>

namespace std
{
template<typena me _Tp, template<typena me> class _Container,
typename _Tpval, typename _BinaryOperatio n>
_Container<_Tp> &
transform(_Cont ainer<_Tp>& __cont, const _Tpval& __val,
_BinaryOperatio n __binary_op)
{
_Container<_Tp> ::iterator __iter=__cont.b egin();
_Container<_Tp> ::iterator __end=__cont.en d();
for ( ; __iter != __end; ++__iter)
*__iter = __binary_op(*__ iter, __val);
return __cont;
}

} //namespace std

#endif //ALGORITHM_EXT_H H

The error message I get from g++ (GCC) 3.3 20030226 (prerelease) (SuSE
Linux) is:
linux@earth:~/> g++ mod2pnm.cc -o mod2pnm
In file included from mod2pnm.cc:16:
algorithm_ext.h h: In function `_Container<_Tp >&
std::transform( _Container<_Tp> &, const _Tpval&, _BinaryOperatio n)':
algorithm_ext.h h:32: error: parse error before `=' token
algorithm_ext.h h:33: error: parse error before `=' token
algorithm_ext.h h: In function `_Container<_Tp >&
std::transform( _Container<_Tp> &, const _Tpval&, _BinaryOperatio n)
[with _Tp
= double, _Container = std::vector, _Tpval = double,
_BinaryOperatio n =
std::minus<doub le>]':
mod2pnm.cc:144: instantiated from here
algorithm_ext.h h:34: error: `__end' undeclared (first use this
function)
algorithm_ext.h h:34: error: (Each undeclared identifier is reported
only once
for each function it appears in.)
algorithm_ext.h h:34: error: `__iter' undeclared (first use this
function)
Any ideas, what's wrong? I tried all night long!

Thanks, Steffen

[WW]

Steffen Brinkmann wrote:

#ifndef ALGORITHM_EXT_H H
#define ALGORITHM_EXT_H H

#include<iterat or>

namespace std
{
You are not allowed to place anything into the std namespace!
template<typena me _Tp, template<typena me> class _Container,
Standard container templates take many more arguments.
typename _Tpval, typename _BinaryOperatio n>
_Container<_Tp> &
transform(_Cont ainer<_Tp>& __cont, const _Tpval& __val,
_BinaryOperatio n __binary_op)
{
_Container<_Tp> ::iterator __iter=__cont.b egin(); typename _Container<_Tp> ::iterator __iter=__cont.b egin();
_Container<_Tp> ::iterator __end=__cont.en d(); Ditto
for ( ; __iter != __end; ++__iter)
*__iter = __binary_op(*__ iter, __val);
return __cont;
}

} //namespace std

#endif //ALGORITHM_EXT_H H

The error message I get from g++ (GCC) 3.3 20030226 (prerelease) (SuSE
Linux) is:

[SNIP]

Seems that 3.3 has two phase name lookup implemented or at least it refuses
to guess what is a type anymore.

--
WW aka Attila

[Howard Hinnant]

Steffen Brinkmann wrote:

I tried to modify the transform algorithm in a way that it doesn't
take iterators, but a reference to a container class and a value,
because Mostly I need to do an operation of a container and a single
number (e.g. multiply all the values in a vector by 3 or so).

In addition to WW's good comments, I thought I might add:

You might try out std::bind2nd in <functional> and stick with the
std::transform:

std::transform( v.begin(), v.end(), v.begin(),
std::bind2nd(st d::multiplies<i nt>(), 3));

If you get into more complicated operations, boost::bind might provide
an answer ( www.boost.org ). boost::bind may eventually be
standardized. It has been voted into the first library technical report
which indicates an official interest in this library. The above
transform translates into bind with:

std::transform( v.begin(), v.end(), v.begin(),
boost::bind(std ::multiplies<in t>(), _1, 3));

-Howard

[David B. Held]

"WW" <wo***@freemail .hu> wrote in message
news:bk******** **@phys-news1.kolumbus. fi...

[...]
You are not allowed to place anything into the std
namespace!
[...]

Except specializations of std::less<>, and perhaps a few other
things.

Dave

[Jerry Coffin]

In article <bk**********@p hys-news1.kolumbus. fi>, wo***@freemail. hu
says...

[ ... ]

You are not allowed to place anything into the std namespace!

Not so -- you are specifically allowed to add (partial or complete)
specializations of standard library templates to namespace std. See $
17.4.3.1/1 for the exact requirements.

--
Later,
Jerry.

The universe is a figment of its own imagination.

[WW]

David B. Held wrote:

"WW" <wo***@freemail .hu> wrote in message
news:bk******** **@phys-news1.kolumbus. fi...

[...]
You are not allowed to place anything into the std
namespace!
[...]

Except specializations of std::less<>, and perhaps a few other
things.

Yeah. But they have to be specializations , not new things. And I prefer to
mentioned them for those, who know they can ask this question. :-)

--
WW aka Attila

[WW]

Jerry Coffin wrote:

In article <bk**********@p hys-news1.kolumbus. fi>, wo***@freemail. hu
says...

[ ... ]

You are not allowed to place anything into the std namespace!

Not so -- you are specifically allowed to add (partial or complete)
specializations of standard library templates to namespace std. See $
17.4.3.1/1 for the exact requirements.

You are not placing them into the standard namespace. They are there and
you are allowed to specialize them. I prefer to put it this way because I
have met people (hearing there is exception) kept putting declarations of
new things there.

--
WW aka Attila

[Rob Williscroft]

WW wrote in news:bk******** **@phys-news1.kolumbus. fi:

David B. Held wrote:

"WW" <wo***@freemail .hu> wrote in message
news:bk******** **@phys-news1.kolumbus. fi...

[...]
You are not allowed to place anything into the std
namespace!
[...]

Except specializations of std::less<>, and perhaps a few other
things.

Yeah. But they have to be specializations , not new things. And I
prefer to mentioned them for those, who know they can ask this
question. :-)

IIUC you can specialize *any* template in namespace std aslong as
the specialization is dependant an a UDT not defined in namespace std.
I.e. this should be Ok:

class myclass {};
namespace std
{
template < typename Alloc >
class vector< myclass, Alloc >
{
};
}

Rob.
--
http://www.victim-prime.dsl.pipex.com/

[WW]

Rob Williscroft wrote:
[SNIP]

IIUC you can specialize *any* template in namespace std aslong as
the specialization is dependant an a UDT not defined in namespace std.
I.e. this should be Ok:

class myclass {};
namespace std
{
template < typename Alloc >
class vector< myclass, Alloc >
{
};
}

Chapter and verse?

--
WW aka Attila

[Rob Williscroft]

WW wrote in news:bk******** **@phys-news1.kolumbus. fi:

Rob Williscroft wrote:
[SNIP]

IIUC you can specialize *any* template in namespace std aslong as
the specialization is dependant an a UDT not defined in namespace std.
I.e. this should be Ok:

class myclass {};
namespace std
{
template < typename Alloc >
class vector< myclass, Alloc >
{
};
}

Chapter and verse?

17.4.3.1/1 - but I missed "... results in undefined ... and unless the
specialization meets the standard library requirements for the original
...." so my example wouldn't be Ok (that "IIUC" wasn't wasted after all).

Rob.
--
http://www.victim-prime.dsl.pipex.com/